In recent years, the improvements in the recording density of magnetic recording media has been dramatic, particularly in the field of magnetic disks, and recent recording densities have particularly increased at an extraordinary rate equivalent to an increase of approximately 100-fold in the last 10 years. Many different technologies are responsible for these huge improvements in recording density, but one of the key technologies has been technology for controlling the sliding characteristics between the magnetic head and the magnetic recording medium.
Since the CSS (contact start-stop) method known as the Winchester system, in which the basic operations involve contact sliding-head lifting-contact sliding between the magnetic head and the magnetic recording medium, has become the main system employed within hard disk drives, sliding of the head on the recording medium has become an unavoidable necessity, and therefore problems relating to tribology between the magnetic head and the magnetic recording medium are currently an unavoidable technical issue. As a result, the abrasion resistance and sliding resistance of the surface of a magnetic recording medium play an important role in determining the reliability of the medium, and intensive efforts continue to be directed towards the development and improvement of protective films and lubricating films and the like for lamination onto the magnetic film.
Various materials have been proposed as protective films for magnetic recording media, but from the overall viewpoints of film formability and durability and the like, carbon films are mainly employed. Carbon films are generally formed by sputtering methods, and the conditions during film formation are vividly reflected in either the corrosion resistance of the carbon film or the CSS characteristics, and are therefore extremely important.
Further, in order to improve the recording density, it is desirable to reduce the flying height of the magnetic head and increase the rotational speed of the medium, and therefore the magnetic recording medium requires a higher level of sliding durability.
On the other hand, in order to reduce spacing loss and thereby increase the recording density, the thickness of the protective film needs to be reduced as far as possible, for example to a film thickness of not more than 100 Å. There are strong demands for a protective film which is not only smooth, but also thin and tough.
However, when a carbon protective film formed by a conventional sputtering film formation method is reduced in thickness as far as possible, for example down to a film thickness of 100 Å or less, the durability of the formed film may be unsatisfactory.
Accordingly, methods that employ sputter method and plasma CVD method are becoming widespread as methods capable of forming carbon protective films having higher strengths than those obtainable using sputtering methods.
However, in those methods where the carbon protective film is formed using sputter method and plasma CVD method, inside the film formation apparatus, carbon is not only formed on the surface of the substrate, but also accumulates on the surfaces of the carrier that supports the substrate. When the amount of this type of carbon accumulated on exposed surfaces increases, factors such as internal stress cause the film formed from the accumulated carbon to peel away from the exposed surface. If the particles of carbon generated as a result of this type of peeling adhere to the substrate surface, then protrusions tend to be formed on the carbon protective film, resulting in localized film thickness abnormalities that can cause product defects. Particularly in those cases where the carbon protective film is formed using a plasma CVD method, the resulting film composed of carbon has a higher degree of hardness and higher internal stress than a carbon protective film formed using a conventional sputtering method, and therefore the amount of generated carbon particles is large, and the type of film thickness abnormalities mentioned above tend to be particularly problematic.
Methods of removing a carbon film accumulated on the surface of a substrate-supporting carrier by ashing the carbon film using an oxygen plasma have been proposed to prevent the generation of the types of particles described above (for example, see Japanese Unexamined Patent Application, First Publication No. Hei 11-229150, and Japanese Unexamined Patent Application, First Publication No. 2002-025047). Further, a treatment for suppressing peeling of accumulated material from an electrode by roughening the surface of the carrier has been used to prevent the peeling of an accumulated film from the surface of a substrate-supporting carrier (for example, see Japanese Unexamined Patent Application, First Publication No. 2006-173343).
Recently, there have been considerable demands for further improvements in the cleanliness of the surface of magnetic recording media in order to enable further improvements in the recording density of the magnetic recording media. However, the methods described above alone are not able to satisfactorily reduce the generation of particles, because although thorough ashing occurs in those regions such as the edges of the carrier where the plasma is readily concentrated, satisfactory ashing tends to be unobtainable in regions where the plasma is less readily concentrated, such as the flat surfaces of the carrier. Accordingly, reducing magnetic recording media defects caused by carbon protective film particles is currently a significant problem.
As described above, one of the causes of particle generation from the carbon protective film is the fact that improving the cleanliness of the carrier that supports the substrate is very difficult, and methods of improving this level of cleanliness have been keenly sought.
Further, according to research conducted by the inventors of the present invention, the carbon film accumulated on the carrier surfaces is not completely removed by the ashing treatment described above, and residues tend to remain on the carrier, mainly on the flat surfaces of the carrier. These residues are transported into other film formation chambers together with the carrier, and have also been confirmed as a component of the outgas emitted inside the vacuum chamber. In order to further increase the recording density of a magnetic recording medium while achieving a stable level of product stability, the emission within the vacuum chamber of components other than the intentionally used process gases must be avoided, and improvements in this area are also required.